The default Home Assistant configuration does not allow running a
reverse proxy in front of the application. To enable this, the
`use_x_forwarded_for` and `trusted_proxies` options have to be set.
Since we want `/var/lib/homeassistant` to be a Btrfs subvolume, we can't
simply include the necessary files in the correct location in the rootfs
image. Instead, we must define "copy tree" (`C`) actions for
`systemd-tmpfiles` to copy them from `/usr/share/factory`.
Unfortunately, `systemd-tmpfiles` considers `v` and `C` actions
conflicting, and thus will not copy the directory contents recursively.
Each file has to be listed explicitly.
Dustin